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Pygmies' small stature evolved many times

“Small is beautiful,” argued the British economist E. F. Schumacher back in the 1970s; although he was referring to ecologically appropriate technologies rather than people, the same might be true for humans living in tropical rainforests. Pygmies, small-statured hunter-gatherers such as this woman from the Batwa people of Uganda pictured above, live in Africa, Asia, and the Americas, and many researchers have suggested that their diminutive size is an evolutionary adaptation to the rigors of rainforest life. But scientists have not been sure to what extent Darwinian natural selection is actually responsible for the Pygmy body type and how many times it has arisen over the course of human evolution. In a new study published online today in the Proceedings of the National Academy of Sciences, an international research team reports on its analysis of the DNA of 169 Batwa people from east central Africa, identifying genetic variations that appear to be closely associated with small size and that were apparently under strong natural selection. But when the team compared the Batwa genomes with those of 74 Pygmies from the Baka people of west central Africa, it found that the two groups had very different genetic profiles, even though they were equally small. The team concludes that the Pygmy body plan probably evolved independently multiple times within Africa, rather than having a single origin that then spread across the continent. And the strong signs of natural selection suggest that being small probably was indeed a specific evolutionary adaptation to life in the tropical rainforests. Leading hypotheses for why a small stature could have been advantageous range from downsizing to deal with food scarcity, better resistance to tropical heat, ceasing growth earlier so they can start reproducing sooner—or a combination of all of these factors.